Cement clinker manufacturing method

Abstract

This reduces Cr6+ while suppressing increases in the color b-value and lightness L-value of cement clinker. [Solution] The present invention proposes a cement clinker manufacturing method for manufacturing cement clinker by firing raw materials to be fired, comprising: feeding a main fuel from the downstream side of a rotary kiln and burning it; and feeding a combustible substance separately from the main fuel from the downstream side of the rotary kiln and burning it, wherein, when the inner diameter of the rotary kiln is D and the length is L, the combustible substance is supplied in the cooling zone of the rotary kiln in the range of 0 ≤ L / D ≤ ​​1.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing cement clinker.

Background Art

[0002] In recent years, in the cement industry, the development of cement clinker using waste and by-products such as industrial waste and general waste as raw materials has been carried out. However, some waste and by-products contain chromium, and when cement clinker is manufactured using this as a raw material, hexavalent chromium (hereinafter, Cr6+) is contained in the obtained cement clinker. When such cement clinker is pulverized and used as cement or a solidifying material, Cr6+ may elute from the cement-applied parts of buildings and the like, causing water pollution, soil pollution, and the like.

[0003] For this reason, it is desirable to reduce the amount (ratio) of Cr6+ contained in cement clinker. In this regard, as a method for reducing Cr6+ in the firing process of cement clinker production, for example, Patent Document 1 discloses promoting the reduction of Cr6+ present in the rotary kiln by supplying a combustible substance to the surface or inside of the fired product at the outlet side (kiln cooling zone) of the fired product in the rotary kiln from the highest temperature point of the raw material, thereby reducing the Cr6+ contained in the cement clinker.

[0004] Also, for example, Patent Document 2 discloses a method of blowing a combustible substance into the kiln while maintaining the quality of the cement clinker by blowing the combustible substance upstream of the kiln cooling zone.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] However, the method disclosed in Patent Document 1 has several drawbacks, including the fact that even within the kiln cooling zone, there is considerable variation in the degree of Cr6+ reduction depending on the injection location, and in some cases, a sufficient Cr6+ reduction effect cannot be obtained, or the color b value and lightness L value increase, leading to a deterioration in the quality of the cement clinker. Furthermore, the method disclosed in Patent Document 2 has the problem that the kiln cooling zone becomes an oxidizing atmosphere, causing Cr to reoxidize to Cr6+, and thus Cr6+ cannot be sufficiently reduced. This invention has been made in view of the above circumstances, and proposes a technology to reduce Cr6+ while suppressing the increase in the color b value and lightness L value of cement clinker. [Means for solving the problem]

[0007] To solve the above problems, the present invention, as an example, A method for producing cement clinker by firing raw materials to be fired, The main fuel is introduced and burned from the downstream side of the rotary kiln, This includes introducing a combustible substance separately from the main fuel from the downstream side of the rotary kiln and burning it, When the inner diameter of the rotary kiln is D and its length is L, the combustible material is supplied to the cooling zone of the rotary kiln in the range of 0 ≤ L / D ≤ ​​1. We propose a method for manufacturing cement clinker.

[0008] Further features relating to the present invention will become apparent from the description herein and the accompanying drawings. Furthermore, aspects of the present invention are achieved and realized by elements and various combinations of elements and by the modes of the hereafter detailed description and the accompanying claims. The descriptions herein are merely typical examples and do not limit in any way the claims or applications of the present invention. [Effects of the Invention]

[0009] According to the present invention, it is possible to reduce Cr6+ in cement clinker while suppressing increases in color b value and lightness L value. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows a schematic configuration example of the cement clinker manufacturing apparatus 10 according to this embodiment. [Figure 2] This figure shows an example of the configuration of the firing section according to Comparative Example 1. [Figure 3] This figure shows an example of the configuration of the firing section according to Comparative Example 2. [Figure 4] This figure shows an example of the configuration of the firing section according to Example 1. [Figure 5] This figure shows an example of the configuration of the firing section according to Example 2. [Figure 6] This table shows the test results for Comparative Examples 1 and 2 and Examples 1 and 2. [Modes for carrying out the invention]

[0011] Embodiments of the present invention disclose a method for producing cement clinker using a rotary kiln. Generally, a method for producing cement clinker includes a rotary kiln preheating step, a cement clinker firing step, and a cement clinker cooling step. When cement clinker is reduced in the firing step, the amount of Cr6+ can be reduced, while the color b value and lightness L value increase. An increase in the color b value and lightness L value results in a deterioration of the quality (visual color) of the cement. Therefore, it is not always better to reduce the amount of Cr6+ as much as possible (there is a trade-off between Cr6+ reduction and an increase in the b value, etc.). Accordingly, this embodiment provides a method for producing cement clinker that makes it possible to balance Cr6+ reduction with an increase in the color b value and lightness L value. The production method will be described in detail below.

[0012] <Outline configuration of a cement clinker manufacturing apparatus>

[0013] FIG. 1 is a diagram showing a schematic configuration example of a cement clinker manufacturing apparatus 10 according to the present embodiment. In FIG. 1, a configuration responsible for processes after the firing process in the rotary kiln is shown.

[0014] The cement clinker manufacturing apparatus 10 includes a rotary kiln 101, a main burner 102 for injecting a main fuel to burn a raw material (a material to be fired), an auxiliary burner 103 for locally reducing the oxygen concentration in the cooling zone of the rotary kiln 101, a discharge port 105 for transferring the fired clinker to a cooling process, a cooler 106 for cooling the clinker that has fallen from the discharge port 105 with air, a thermometer 107 for measuring the temperature inside the rotary kiln 101 and the temperature of the discharge port 105, and a control device (for example, configured by a computer) 108.

[0015] Here, the cooling zone of the rotary kiln 101 refers to a part from a position showing the highest temperature in the rotary kiln 101 (the firing point: for example, a position around L / D = 3 from the outlet of the rotary kiln 101; L and D are as follows) to the discharge port 105 of the rotary kiln.

[0016] The auxiliary burner 103 blows a combustible substance into the reduction position 104 and burns it. In the present embodiment, when the inner diameter of the rotary kiln 101 is D and the length of the rotary kiln 101 is L, the reduction position 104 is set so that the flame of the auxiliary burner 103 enters the range of 0 ≦ L / D ≦ 1. That is, in the firing process of cement clinker production, by supplying a combustible substance to the surface or inside of the material to be fired in the range of 0 ≦ L / D ≦ 1, a locally relatively (lower than other parts of the rotary kiln 101) low oxygen concentration environment is created, and while suppressing an increase in the b value and L value of the color tone of the material to be fired, Cr6+ (hexavalent chromium) contained in the cement clinker can be reduced.

[0017] Also, the temperature at the discharge port 105 is set to be a predetermined degree higher than (i) the temperature of the discharge port in the case where the auxiliary burner 103 is not provided (conventional example), or (ii) the temperature of the discharge port when the amount of Cr6+ contained in the cement clinker after once performing the firing process (firing process in the past in terms of time series) is larger than a predetermined value (predetermined amount) (for example, a temperature difference of 50°C: the temperature difference is not limited to 50°C, and any increase will show an effect. The value of the discharge port temperature can be set to, for example, 1300°C to 1350°C). By doing so, it becomes possible to further suppress the increase in the color tone b value and the lightness L value.

[0018] As means for increasing the temperature of the discharge port 105, for example, (i) the main burner 102 is arranged closer to the outlet (discharge port) of the cement kiln 101 so that the temperature of the discharge port 105 becomes about 50°C higher than that of the conventional example (while measuring the discharge port temperature with the thermometer 107, the position of the main burner 102 is adjusted), or when the position of the main burner 102 is not changed, (ii) the suction amount of air is changed by a fan (not shown) to adjust the amount of gas and air in the rotary kiln 101 and change the shape of the flame (e.g., a flame with a short length), or (iii) the rotation speed of the rotary kiln 101 is increased to increase the temperature of the fired product, thereby increasing the discharge port temperature.

[0019] The cooler 106 cools the cement clinker that has fallen from the discharge port 105 with air.

[0020] The thermometer 107 can use, for example, a radiation thermometer to measure the temperature inside the rotary kiln 101 and the temperature of the discharge port 105, and supply the measured value to the control device 108.

[0021] The control device 108 adjusts the heat output of the main burner 102 based on the temperature inside the rotary kiln 101 measured by the thermometer 107. The control device 108 also adjusts the amount of combustible material injected into the auxiliary burner 103 in accordance with the adjustment of the heat output of the main burner 102. The amount of combustible material injected into the auxiliary burner 103 can be, for example, about 5% of the heat output of the main burner 102, but this depends on the amount of Cr contained in the raw material and the properties of the combustible material being injected, so it may be adjusted each time. Furthermore, the control device 108 may adjust the heat output of the main burner 102, the amount of combustible material injected into the auxiliary burner 103, and the position of the main burner 102 according to the operator's instructions input based on the amount of Cr contained in the raw material and the amount of Cr6+ contained in the cement clinker (which can be measured by a pack test). For example, if a pack test reveals that the amount of Cr6+ (including the b-value and L-value) is above a predetermined value, the operator can instruct the control device 108 to increase the ratio of the heat output of the auxiliary burner 103 to that of the main burner 102. On the other hand, if the pack test reveals that the amount of Cr6+ is below a standard value, the heat output of the auxiliary burner 103 is too high and may be reduced. Also, since the pack test has a lower limit, if the Cr6+, b-value, or L-value is below the lower limit, the heat output of the auxiliary burner 103 (the ratio of the heat output to that of the main burner 102) may be increased. Here, the pack test refers to, for example, a product of type: WAK-Cr6+ (Kyoritsu Chemical Research Institute Co., Ltd.). This pack test uses the color development principle of the diphenylcarbazide absorbance spectrophotometric method as defined in JIS K 0102 65.2.1, and allows for the simple measurement of Cr6+ in the water sample with minimal operation.

[0022] <Examples> (i) Material As a raw material for the cement clinker, clinker manufactured at a cement plant was used. In addition, heavy oil was used as the flammable substance blown in from the auxiliary burner 103. As the flammable substance, substances containing at least one of the following may also be used: bituminous coal, coke, waste plastics, flammable waste, heavy oil, heavy oil sludge, or crude oil sludge.

[0023] (ii) Method for evaluating cement clinker The amount of water-soluble Cr6+ was analyzed using the JCAS I-53 method. Furthermore, the color b value and lightness L value were determined using a Blaine specific surface area of ​​3300 ± 100 cm². 2 The Hunter Lab was measured using a spectrophotometer on a sample (cement clinker) that had been ground to a density of / g.

[0024] (iii) Test method

[0025] In this test, both Comparative Examples 1 and 2 and Examples 1 and 2 used a rotary kiln 101 with a maximum temperature point (burning point) of approximately 1450°C. Here, if the inner diameter of the rotary kiln 101 is D and the length in the longitudinal direction is L, the burning point was set to approximately L / D = 3 from the kiln outlet, and the area from the burning point to the kiln outlet 105 (0 ≤ L / D ≤ ​​3) was defined as the kiln cooling zone.

[0026] (Comparative Example 1) Figure 2 shows an example of the firing section configuration according to Comparative Example 1. In Comparative Example 1, the clinker is fired using only the main burner 102, without using the auxiliary burner 103. The firing point is set to approximately L / D=3 from the kiln outlet, as described above.

[0027] (Comparative Example 2) Figure 3 shows an example of the calcination section configuration according to Comparative Example 2. In Comparative Example 2, clinker is calcined using a main burner 102 and an auxiliary burner 103. In Comparative Example 2, the reduction position 104 (the position where the combustible material is injected) is set within the range of 1 ≤ L / D ≤ ​​2 in the kiln cooling zone (the position of the tip of the auxiliary burner 103 is set to L / D=1, and the position of the flame tip is set to L / D=2). In Comparative Example 2 (and similarly in Examples 1 and 2), the amount of combustible material (heavy oil) injected from the auxiliary burner 103 is approximately 5% of the heat used by the main burner 102. However, the actual amount injected may be adjusted each time, as it depends on the amount of Cr contained in the raw material clinker and the properties of the combustible material being injected.

[0028] (Example 1) Figure 4 shows an example of the configuration of the firing section according to Example 1. In Example 1, the clinker is fired using the main burner 102 and the auxiliary burner 103, similar to Comparative Example 2. However, by setting the position of the tip of the auxiliary burner 103 to L / D=0 and the position of the flame tip to L / D=1, the reduction position 104 (the position where the combustible material is injected) is set to 0≦L / D≦1.

[0029] (Example 2) Figure 5 shows an example of the configuration of the firing section according to Example 2. In Example 2, the clinker is fired using the main burner 102 and the auxiliary burner 103, similar to Example 1. By setting the position of the tip of the auxiliary burner 103 to L / D=0 and the position of the flame tip to L / D=1, the reduction position 104 (the position where the combustible material is injected) is set to 0≦L / D≦1. However, the difference from Example 1 is that the main burner 102 is positioned so that the position of the tip of the main burner 102 is closer to the downstream side of the rotary kiln 101. As a result, the dropout temperature is raised by 50°C compared to Example 1. In this test, the dropout temperature was adjusted by adjusting the position of the main burner 102, but this is not the only way to adjust the dropout temperature. For example, it is possible to adjust the burner flame to a short flame, or to add a sub-burner (not shown) near the dropout and heat it. (iv) Test results

[0030] Figure 6 is a table showing the test results for Comparative Examples 1 and 2 and Examples 1 and 2. In Figure 6, the outlet temperature difference represents the outlet temperature difference compared to no reduction (Comparative Example 1). The L value increase rate, b value increase rate, and Cr6+ reduction rate are calculated as the percentage increase or decrease for Comparative Example 2, Example 1, and Example 2 compared to no reduction (Comparative Example 1). From this, the increase rates of the L value and b value relative to the Cr6+ reduction rate for Comparative Example 2, Example 1, and Example 2 (L value increase rate / Cr6+ reduction rate and b value increase rate / Cr6+ reduction rate) are shown.

[0031] As shown in Figure 6, in Comparative Example 2, in which a combustible substance was injected at a position of 1 ≤ L / D ≤ ​​2, the increase rates of L and b values ​​relative to the Cr6+ reduction rate were 8.1 and 9.7, respectively, compared to Comparative Example 1, in which no combustible substance was injected by the auxiliary burner 103.

[0032] On the other hand, in Example 1, where the flammable material was blown into a position where 0 ≤ L / D ≤ ​​1, the increase rates of L and b values ​​relative to the Cr6+ reduction rate were lower at 3.7 and 5.5, respectively, compared to Comparative Example 2. Furthermore, in Example 2, where the flammable material was blown into a position where 0 ≤ L / D ≤ ​​1, similar to Example 1, but the outlet temperature was increased by 50°C, the increase rates of L and b values ​​relative to the Cr6+ reduction rate were even lower at 1.8 and 2.6, respectively.

[0033] This result is thought to be related to the ferrite phase, a colored mineral contained in the cement clinker product. Generally, it is known that when the crystallization temperature range of the ferrite phase (approximately 1200°C to 1335°C) is slowly cooled, the crystallinity of the ferrite phase increases and the amount of solid solution components such as MgO decreases, resulting in an increase in the L and b values. Furthermore, as in Comparative Example 2, when a combustible material was blown into the area 0 ≤ L / D ≤ ​​2 and Cr6+ was reduced, the subsequent slow cooling in the 0 ≤ L / D ≤ ​​1 range in a high-oxygen atmosphere caused an increase in color tone, and Cr was also re-oxidized to Cr6+, which is presumed to have increased the rate of increase in the L and b values ​​relative to the Cr6+ reduction rate.

[0034] On the other hand, in Example 1, the position 0 ≤ L / D ≤ ​​1 was reduced, and then the cement clinker was rapidly cooled. This suppressed re-oxidation to Cr6+, which is thought to have resulted in a lower increase in the L and b values ​​relative to the Cr6+ reduction rate. Furthermore, in Example 2, where the outlet temperature was increased, the cement clinker was rapidly cooled from a higher temperature than in Example 1 (outlet temperature: approximately 1350°C). This completely rapid cooled the crystallization temperature range of the ferrite phase, further suppressing the increase in color tone, and thus resulting in an even lower increase in the L and b values ​​relative to the Cr6+ reduction rate.

[0035] Based on the above, in the firing process of cement clinker production, by supplying a combustible substance to the surface or interior of the workpiece in the range of 0 ≤ L / D ≤ ​​1, it is possible to create an environment with a relatively low oxygen concentration locally, thereby suppressing the rise in color of the workpiece while reducing Cr6+ and producing cement clinker. Furthermore, by increasing the discharge temperature when supplying a combustible substance to the surface or interior of the workpiece in the range of 0 ≤ L / D ≤ ​​1, it is possible to further suppress the rise in color of the workpiece while reducing Cr6+.

[0036] <Summary> (i) In the cement clinker manufacturing method according to this embodiment and example, the main fuel is introduced and burned from the downstream side of the rotary kiln 101, and a combustible substance is introduced and burned separately from the main fuel from the downstream side of the rotary kiln 101. At this time, when the inner diameter of the rotary kiln 101 is D and the length is L, the combustible substance is supplied in the cooling zone of the rotary kiln 101 in the range of 0 ≤ L / D ≤ ​​1 (reduction position). By doing so, it is possible to create an environment with a relatively low oxygen concentration locally (at the reduction position), so that it is possible to reduce Cr6+ while suppressing the increase in the color b value and lightness L value of the cement clinker. Combustion by introducing the main fuel is performed by the main burner 102, and combustion by introducing the combustible substance is performed by the auxiliary burner 103.

[0037] (ii) In addition to (i) above, the temperature of the outlet 105 of the rotary kiln 101 may be further adjusted (the outlet temperature may be set higher than when the outlet temperature is not adjusted (in the cases of Comparative Examples 1 and 2 and Example 1)) (Example 2). More specifically, if the value of Cr6+ contained in the cement clinker obtained by firing the raw materials to be fired is higher than a predetermined value (for example, by measuring the amount or percentage of Cr6+ in a pack test), the outlet temperature may be set higher than the outlet temperature in that case. By doing so, it is possible to maintain a high reduction rate of Cr6+ while keeping the increase rate of the color b value and lightness L value low.

[0038] Methods for increasing the discharge temperature include keeping the flame of the main burner 102 the same as in Comparative Example 1, etc., while moving the tip of the main burner 102 closer to the downstream side of the rotary kiln 101, making the flame of the main burner 102 shorter than the flame in Comparative Example 1, etc. (the flame when the discharge temperature is not adjusted according to the value of Cr6+ contained in the cement clinker), or heating the discharge 105 using a local heating sub-burner (not shown) different from the main burner 102 and auxiliary burner 103. This makes it possible to increase the discharge temperature while keeping the firing temperature as constant as possible (keeping the firing temperature as similar as possible before and after adjusting the discharge temperature according to Cr6+).

[0039] (iii) The flammable material may be a substance containing at least one of the following: bituminous coal, coke, waste plastics, flammable waste, heavy oil, heavy oil sludge, or crude oil sludge.

[0040] (iv) The amount of heat obtained by burning the above-mentioned combustible material may be 5% of the amount of heat obtained by inputting the main fuel when carrying out the firing process. However, the above ratio of the amount of heat obtained by burning the combustible material will vary depending on the amount of Cr contained in the raw material to be fired and the properties of the combustible material to be input, so it may be adjusted each time based on the results of pack tests, etc. [Explanation of Symbols]

[0041] 10. Cement clinker manufacturing apparatus 101 Rotary Kiln 102 Main Burner 103 Auxiliary burner 104 Reduction position 105 Ochiguchi 106 Cooler 107 Thermometer 108 Control device

Claims

1. A method for producing cement clinker by firing raw materials to be fired, The main fuel is introduced and burned from the downstream side of the rotary kiln, This includes introducing a combustible substance separately from the main fuel from the downstream side of the rotary kiln and burning it, When the inner diameter of the rotary kiln is D and its length is L, the combustible material is supplied to the cooling zone of the rotary kiln in the range of 0 ≤ L / D ≤ ​​1. Method for manufacturing cement clinker.

2. In claim 1, Combustion by introducing the aforementioned main fuel is carried out by the main burner. A method for producing cement clinker, wherein combustion by introducing the aforementioned combustible substance is carried out by an auxiliary burner separate from the main burner.

3. In claim 1, further, This includes adjusting the temperature of the outlet of the rotary kiln according to the value of Cr6+. A method for producing cement clinker, wherein the temperature of the outlet is made higher than the temperature when the outlet temperature is not adjusted according to the value of Cr6+.

4. In claim 3, A method for producing cement clinker, comprising adjusting the temperature of the outlet by moving the tip of the main burner closer to the downstream side of the rotary kiln, while keeping the flame of the main burner that burns the main fuel the same as the flame when the temperature of the outlet is not raised.

5. In claim 3, A method for producing cement clinker, wherein the flame of the main burner that burns the main fuel is shorter than the flame when the temperature of the outlet is not high.

6. In claim 3, A method for producing cement clinker, comprising heating the outlet using a sub-burner for local heating, which is different from the main burner for burning the main fuel and the auxiliary burner for burning the combustible substance.

7. In claim 1, A method for producing cement clinker, wherein the combustible substance includes at least one of bituminous coal, coke, waste plastic, combustible waste, heavy oil, heavy oil sludge, or crude oil sludge.

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